docs: def rest_api_url(self, *url_parts, **kwargs):
          """Join the URL of REST_API
  
          parameters:
              upl_parts:  strings that are joined to the url by "/".
                  a REST url like https://na1.salesforce.com/services/data/v44.0/
                  is usually added, but not if the first string starts with https://
              api_ver:  API version that should be used instead of connection.api_ver
                  default. A special api_ver="" can be used to omit api version
                  (for request to ask for available api versions)
              relative: If `relative` is true then the url is without domain
          Examples: self.rest_api_url("query?q=select+id+from+Organization")
                    self.rest_api_url("sobject", "Contact", id, api_ver="45.0")
                    self.rest_api_url(api_ver="")   # versions request
                    self.rest_api_url("sobject", relative=True)
                    self.rest_api_url("/services/data/v45.0")
          Output:
  
                    https://na1.salesforce.com/services/data/v44.0/query?q=select+id+from+Organization
                    https://na1.salesforce.com/services/data/v45.0/sobject/Contact/003DD00000000XYAAA
                    https://na1.salesforce.com/services/data
                    /services/data/v45.0
                    https://na1.salesforce.com/services/data/44.0
          """
          url_parts = list(url_parts)
          if url_parts and re.match(r'^(?:https|mock)://', url_parts[0]):
              return '/'.join(url_parts)
          relative = kwargs.pop('relative', False)
          api_ver = kwargs.pop('api_ver', None)
          api_ver = api_ver if api_ver is not None else self.api_ver
          assert not kwargs
          if not relative:
              base = [self.sf_session.auth.instance_url]
          else:
              base = ['']
          if url_parts and url_parts[0].startswith('/'):
              prefix = []
              url_parts[0] = url_parts[0][1:]
          else:
              prefix = ['services/data']
              if api_ver:
                  prefix += ['v{api_ver}'.format(api_ver=api_ver)]
          return '/'.join(base + prefix + url_parts)